Current wireless technology trends towards increasing numbers of wireless standards and radio frequency (RF) bands to support wireless communications have led to the development of multi-standard, multi-band cellular systems. Such efforts have produced well-performing wideband receivers and frequency synthesizers. However, power amplifiers having the desired performance, e.g., Power-Added Efficiency (PAE), output power, etc., across the multiple frequency bands remains a challenge for such cellular systems.
While various groups have attempted to solve this problem, the results generally do not provide sufficient efficiency across a wide frequency band, undesirably require multiple amplifier stages, do not provide wideband operation, etc. For example, “A Polyphase Multipath Technique for Software-Defined Radio Transmitters” by R. Shrestha, E. A. M. Klumperink, E. Mensink, G. J. M. Wienk, and B. Nauta (IEEE J. Solid-State Circuits, vol. 41, no. 12, pp. 2681-2692, 2006) provides a wideband solution, but the output power is insufficient and the efficiency across the wideband is low relative to single band amplifiers. “A 1.9 GHz 1 W CMOS Class E Power Amplifier for Wireless Communications” by K. C. Tsai and P. R. Gray (ESSCIRC, pp. 76-79, 1998), referred to herein as the Tsai solution, and “A 29 dBm 70.7% PAE Injection-Locked CMOS Power Amplifier for PWM Digitized Polar Transmitter” by J. Paek and S. Hong (Microwave and Wireless Components Letters, vol. 20, no. 11, pp. 637-639, 2010), referred to herein as the Paek solution, provide alternative solutions using injection-locked power amplifiers. These solutions, however, require multiple amplifier stages and have not shown wideband frequency operation. Another solution, “A 65 nm CMOS 30 dBm Class-E RF Power Amplifier with 60% Power Added Efficiency” by M. Apostolidou, M. P. van der Heijden, D. M. W. Leenaerts, J. Sonsky, A. Heringa, and I. Volokhine (Radio Frequency Integrated Circuits Symposium, pp. 141-144, 2008), referred to herein as the Apostolidou solution, provides a wideband solution with improved PAE and output power, but requires multiple amplifier stages, which undesirably increases the chip area and power consumption of the amplifier.
Thus, there remains a need for an improved power amplifier useful in wideband RF scenarios.